The present invention relates to a driving/steering axle for motor vehicles. In particular, the invention concerns a driving/steering axle having a differential, two transmission lines which originate from the differential and which are each adapted for driving a drive and steering wheel, each transmission line including an input shaft which is connected to the differential, an output shaft which is connected to the corresponding drive wheel, a wheel pivot having an axis which is orientated transversely to each of the input shaft and the output shaft, and a double joint for torque transmission between the input shaft and the output shaft. The input and output shafts are guided directionally in space independently of the double joint. The double joint is arranged substantially perpendicularly to the pivot and includes two elementary joints which are connected axially to each other along a double joint axis and which each have an elementary breaking center.
This type of axle is used in the field of motor vehicles of the all wheel drive type, such as industrial vehicles, farm tractors or “4×4” touring vehicles. This type of vehicle comprises at least one such driving/steering axle, commonly known as a “rigid axle”, which is provided with a differential and which can simultaneously transmit, from the differential casing, a drive torque to each wheel, with which each of the ends thereof is provided, and to allow the steering lock of these wheels when the vehicle has to change direction. In more precise terms, such a driving/steering type axle comprises:                an axle member which acts as a beam and which is constituted by a central casing which is provided with a differential assembly and the support bearings thereof and which is extended by two lateral flared tubes, one per side of the vehicle, each of them terminating in a directionally pivoting jaw; an input shaft is arranged in each flared tube and is supported, at the jaw side, by a bearing and, at the differential side, by a corresponding planetary gear of the differential assembly, to which it is fixedly joined in terms of rotation by ribs;        a wheel hub, at each side of the vehicle, which supports the wheel by means of bearings, the wheel receiving the rotation movement thereof from a spindle which extends through it and which forms an output shaft; the wheel hub is itself also provided with a pivoting jaw, which is associated with that of the flared tube of the axle member, along a substantially vertical pivot axis arrangement, commonly known as the “wheel pivot”; and        an articulation which ensures the transmission of the torque from the input shaft which is positioned in the flared tube of the axle member to the wheel spindle, whether the wheel is straight or pivoted, and which is positioned perpendicularly to the axis arrangement of the wheel pivot.        
Until now, various articulations have been used to ensure the transmission of torque at the wheel pivot. At first, for example, double-joint articulations having a cardan type kinematic arrangement were preferred, the spacing between the articulation centers of the elementary joints of the double joint being constant, such as the Richard Bussien articulations described, for example, in U.S. Pat. Nos. 1,847,749 and 2,084,429.
Subsequently, the use of articulations having double joints constituted by two fixed cardan type elementary joints became widespread.
In all cases, these articulations bring about a translation movement of one of the shafts during the steering lock of the wheels and therefore during the breaking of the double joint. This movement is absorbed either by the driving ribs of the planetary gear of the differential (input shaft) or by those of a wheel reduction gear (output shaft), which produces additional mechanical stresses which are detrimental to the correct operation and the reliability of the articulation, both in the region of the double joint and the sealing members and the support means for the shafts, such as the bearings thereof.
Furthermore, the articulations having two fixed cardan type joints, in a so-called “W” configuration, have the disadvantage of a high loss in torque transmission when the breaking angle formed between the axes of the input shaft and output shaft deviates from an angle of zero.
The object of the invention is to provide a driving/steering axle of the type set out above whose mechanical characteristics, in particular in terms of friction, noise and vibrations, are improved.